Fetching one to many relationship data with Core Data

Question

I have a Core Data model with an entity called SeasonInfo that contains a bunch of attributes, one of which is an attribute called year (int 16). SeasonInfo contains a one-to-many relationship to an entity called GameInfo (the relationship name defined in SeasonInfo is called games).

My populated database contains a bunch of seasons (one for every year)... then each season has a list of games - a bunch of games for each season. SeasonInfo <---->> GameInfo

In my TableView contoller I use the following to access the SeasonInfo for a given year :

NSFetchRequest *fetchRequest = [[NSFetchRequest alloc] init];
NSEntityDescription *entity = [NSEntityDescription
                               entityForName:@"SeasonInfo"      inManagedObjectContext:managedObjectContext];
[fetchRequest setEntity:entity];

// Set up the cell...
SeasonInfo *info = [seasonInfoArray objectAtIndex:indexPath.row];

//Put the Year as the Main title of the Row
yearLabel.text =[NSString stringWithFormat: @"%@",   info.year];

That seems to work great... but now I can't figure out how to access the games for a specific season. From this table view, when I select a specific year, I'd like to pass an NSArray of games to another Table View controller... I know how to pass data between views, I just can't figure out how to populate the "gamesArray" before I transition to the Schedule View.

Answer 1

If you've created the relationships properly in Core Data then you can just access the games relationship by it's property.

So info.games should return an NSSet of GameInfo for that SeasonInfo.

Answer 2

If you only need to fetch the games for a specific season then you can use a predicate before you fetch such as (this only works for int 32, change string format specifier (%d) to whatever you need for an int16):

NSPredicate *equalPredicate =[NSPredicate predicateWithFormat:@"year == %d", year]; [fetchRequest setPredicate:equalPredicate];

If you don't want to do that and want everything to be collected then after your executeFetchRequest completes and you're in the successful completion block you will have been provided a NSArray * of results.

for (SeasonInfo * seasonInfo in results)
{
    if ([seasonInfo year] == <whatever year you want>)
    {
        //save this seasonInfo for use, this contains the games you're interested in.
    }
}

Afterwards, to get at the specific games in the seasonInfo

for (GameInfo * gameInfo in [seasonInfo games])
{
   // Do what's needed with the gameInfo.

}